Compressive Fatigue Strength Research Articles

Fatigue life assessment of carbon nanotubes reinforced Al‐Cu‐Mg composite foams via statistics analysis and computer vision

AbstractThe unsatisfactory fatigue performance of Al foams significantly limits their engineering applications. Meanwhile, the unique pore structure of metal foams makes it still challenging to assess its fatigue. Herein, we report an innovative strategy for preparing carbon nanotubes reinforced Al‐Cu‐Mg (CNTs/Al‐Cu‐Mg) composite foams, which exhibit superior compressive strength (16.17 MPa) and fatigue strength (11.17 MPa). Statistics analysis confirms that the fatigue life (Nf) follows Weibull distribution, and P‐S‐N curves were obtained to calculate the theoretical stress level required to achieve the expected Nf. Moreover, computer vision is utilized to monitor the fatigue deformation process and effectively detect fatigue crack initiation sites. Notably, the accuracy of predicted Nf obtained by this method is exceptionally high (98.32%). This work provides a theoretical and practical basis for designing metal foams with superior fatigue properties and offers a promising bottom‐up tactic for predicting the Nf of metal foams to prevent fatigue failure.

Preparation of PEG/P(U-AM-ChCl) composite hydrogels using ternary DES light polymerization and their properties.

Deep eutectic solvents (DES) were prepared using urea (U) and acrylamide (AM) as hydrogen bond donors (HBD) and choline chloride (ChCl) as hydrogen bond acceptor (HBA), and polyethylene glycol (PEG) was selected as a filler and uniformly dispersed in DES to prepare PEG/P(U-AM-ChCl) composite hydrogels by light polymerization. The composite hydrogels were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The effects of the content of PEG on the swelling properties, mechanical properties and fatigue resistance of the composite hydrogels were investigated. The results showed that the compressive strength and fatigue strength of the composite hydrogels were gradually enhanced with the increase of the PEG content in the composite hydrogels, in which the maximum compressive strength of the hydrogels with 1 wt% PEG added was increased by 1.86 times. The composite hydrogel had excellent swelling properties, and the equilibrium swelling degree of the hydrogel with 1 wt% PEG added reached 10.15. Meanwhile, the PEG/P(U-AM-ChCl) composite hydrogel had excellent self-healing properties, and the self-healing rate of the composite hydrogel with a PFG content of 1 wt% could reach 91.93% after 48 hours of healing. This study provides a convenient and efficient method to prepare composite hydrogels with superior swelling properties and self-healing properties.

Compressive fatigue behavior of graded tantalum scaffolds produced by electron beam powder bed fusion

In this study, graded tantalum scaffolds were manufactured by electron beam powder bed fusion (EB-PBF). Compression-compression fatigue testing was conducted on the EB-PBF built graded tantalum scaffolds. The compressive fatigue behavior and compressive fatigue strength of graded tantalum scaffolds with vertical gradient (VG) and parallel gradient (PG) states were investigated. In the fatigue testing, the failure of PG graded scaffold was concentrated on the lowest strength constituent, resulting in higher cyclic ratcheting strain and fatigue damage strain. In terms of the VG graded scaffold, due to the simultaneous uniform deformation of each structure, the strain accumulation in a single cycle was small, resulting in the low cyclic ratcheting strain. In addition, the propagation of fatigue cracks in pore structure with higher strength can be retarded by the stress redistribution, resulting in the low fatigue damage strain. Therefore, the design idea of graded pore structure under identical strain condition is beneficial to obtain porous tantalum scaffold with high compressive fatigue strength.

Comparison of compressive fatigue performance of cementitious composites with different types of carbon nanotube

The compressive fatigue performance of cementitious composites largely depends on the generation and connection of fatigue nano/micro-cracks in the composites. These types of cracks are beyond the scope that traditional fibers can restrain, but can be effectively eliminated and inhibited by incorporating nano-materials, especially those with fiber shape, such as carbon nanotube (CNT). Unfortunately, the effect of CNT and its physical and chemical characteristics on the compressive fatigue performance of cementitious composites remains unclear. Therefore, this paper systematically investigated the effect of CNT with different contents and sizes, functional groups and coating layers on the compressive fatigue performance of cementitious composites, including fatigue life, strength, deformation behavior and cracking characteristics. The morphology of the fatigue fracture surface of cementitious composites shows that CNT can refine pore structure, bridge nano/micro-cracks and result in the generation of the multi-directional and network-like fatigue micro-cracks as well as the appearance of the fatigue striation around aggregates. Consequently, by increasing the integrity among each phase of cementitious composites, CNT significantly maximizes the compressive fatigue life (in logarithmic form), strength and failure strain of cementitious composites by 160 %, 43.4 % and 20.6 %, respectively, showing great potential for extending the service life of concrete structures.

Influence of Process Parameters of Unidirectional Glass Fiber Fabric on Resin Infiltration Rate

The tensile and compressive strength, torsional strength, and fatigue strength of wind turbine blades are closely related to the infusion defects during the manufacturing process of blade girders. Inadequate understanding of the resin infiltration process of the glass fiber fabric is one of key factors leading to the infusion defects. This article mainly studies the influence of fabric weft TEX, weft angle, stitch length, and stitch tension on the resin infiltration rate through experiments. The results show that the resin infiltration rate in the 90° direction of fabric increases as weft TEX and weft angle increase and that the infiltration rate in the thickness direction increases when stitch length and stitch tension increase.

Processing, structure, and properties of additively manufactured titanium scaffolds with gyroid-sheet architecture

While the relationships between processing, structure, and properties of solid titanium alloys produced by additive manufacturing have been established, these relationships are less understood for porous materials, particularly those with rough surfaces inherent to L -PBF. For orthopedics applications, porous architecture and surface roughness are desirable for bone growth, and thus optimization of fatigue life despite these inherent fatigue drivers is critical. The present results establishes relationships between post-processing, microstructure, and resulting fatigue properties for gyroid-sheet scaffolds with as-fabricated surfaces. By comparison of known factors driving fatigue behavior, the relative effect of each on normalized fatigue strength was quantified. Normalized compressive fatigue strength of the gyroid-sheet scaffolds which underwent no surface treatments was observed to be > 50%. The result is higher than that seen for tension fatigue of analogous gyroid-sheet scaffolds, or compared to previously reported normalized compressive fatigue strength of strut based scaffolds. The high strength and fatigue resistant behavior of gyroid-sheet scaffolds despite the inherent surface roughness of L -PBF is desirable for biomedical applications.

Development of fiber Bragg grating strain sensor with temperature compensation for measurement of cryogenic structures

It is important to discriminate between mechanical strain and thermal output (apparent strain) in fiber Bragg grating (FBG) strain sensors, due to their sensitivity to both mechanical strain and thermal output. Additionally, when FBG sensors are directly bonded on monitored structures, the transverse effect and the strain-transfer error must be considered to correctly measure the strain. The objectives of this study are to develop pre-tension packaged FBG strain sensors with temperature compensation for use in cryogenic environments and to clarify the performance of the developed sensors in the range from room temperature to 4 K. A developed FBG sensor comprises sensor mounting parts and two FBG that are placed in a row on a single fiber. The one of the FBGs is a strain sensor and the other is a temperature compensation sensor. The developed FBG sensor intrinsically prevents both the transverse effect and the strain transfer error. Experimental investigations are conducted to clarify the performance in the temperature range from room temperature to 4 K for the developed FBG strain sensors. Results confirm that the developed FBG strain sensor demonstrates superior gauge factor stability and a reasonable temperature compensation function. Moreover, the compressive fatigue strength of the developed FBG strain sensor is investigated due to its importance in cryogenic structures that are subjected to cyclic compressive deformations by the repeated operation of cooling and warming processes.

Experimental and numerical investigation on compressive fatigue strength of lattice structures of AlSi7Mg manufactured by SLM

Micro-lattice materials represent nowadays a great opportunity for developing new ultra-lightweight materials. Design flexibility and multi-functional properties make them attractive for several applications in automotive, medical, space, aerospace and process industries. Predict fatigue resistance of these micro-structures is a key issue. In this work three different unit cells printed by a Selective Laser Melting process with an AlSi7Mg powder were analysed. Static properties and fatigue strength in compression have been studied by means of different experimental and numerical techniques: experimental tests, Digital Image Correlation, Micro-Computed Tomography and Finite Element analysis. Total fatigue life has been divided in three stages: ratcheting, damage initiation and propagation in one or few struts leading to final failure. The experimental results show that the initial ratcheting strain rate is significantly correlated to the life of each sample. The damage maps show that, even at fatigue limit, crack propagation in one or few struts is expected to occur. The effect of defects and local irregularities on the fatigue strength has been studied by means of finite elements models based on the as-manufactured geometry of the samples and on the definition of an equivalent stress amplitude based on a multiaxial high cycle fatigue criterion. A correlation between broken struts and maximum values of local equivalent fatigue stress amplitude has been demonstrated by post-test tomographies.

Laboratory investigation of the Skl-style fastening system’s lateral load performance under heavy haul freight railroad loads

Throughout the international railway community, there are many different designs of elastic fastening systems that have been developed to meet a variety of design specifications and performance expectations. Historically, in North America, the most common types of fastening systems used for concrete crossties are the Safelok I or e-clip systems. In recent years railroads have begun implementing the Skl-style (W) fastening system with concrete crossties in existing and new heavy haul freight railroad mainlines. The magnitude of lateral force applied to the Skl-style fastening system is important information for both design and application purposes. Despite this importance, the lateral force applied to the Skl-style fastening system in a heavy haul freight railroad environment has never been quantified to date. To better understand how the Skl-style system performs under the magnitude of lateral loads observed on heavy haul freight railroads, research was conducted by the Rail Transportation and Engineering Center (RailTEC) at the University of Illinois at Urbana-Champaign (UIUC). The focus of this paper is on laboratory characterization of the lateral load path through the Skl-style fastening system using novel instrumentation techniques that are subjected to heavy haul freight railroad loading conditions. The investigation of fastening system performance included an evaluation of lateral load distribution through the track superstructure, and a single fastening system. Laboratory experimentation concluded that lateral wheel load is primarily distributed to three crossties, the relationship between lateral wheel load and lateral force resisted by field side angled guide plate is non-linear, and that the design of the Skl-style fastening system allows lateral force to be transferred into the crosstie below the worst case concrete compressive fatigue strength. The observations from this study will assist the rail industry in improving fastening system design and developing mechanistic track structure design method.

Influence of Antibiotics Addition in Bone Cements for Hip Arthroplasty on their Mechanical Properties: Clinical Perspective and<i> In Vitro</i> Tests

Bone cement has been used for over half a century, to successfully anchor artificial joints. From its emergence there have appeared a number of types of bone cement, with the 2 major classes being bone cement with or without active substances. The one with the added antibiotics is used primarily in the treatment and revision surgery of infected total hip arthroplasty (THA), as well as a prophylactic method in primary THA in patients with high risks for this complication. The purpose of this study is to determine the mechanical properties of bone cement with added antibiotics. Over a period of 2 years, a number of 41 cases were chosen for this study: 25 with revision surgery for THA, where bone cement with antibiotics was used, and 16 with primary THA, where regular bone cement was used. A number of studies have been performed on the mechanical properties of the 2 types of cement, which determined that the cement with antibiotics presents a slightly lower compressive strength, tensile strength, elastic modulus and fatigue strength compared with regular cement. These variations, however, become more pronounced as the quantity of the antibiotic goes up. The mechanical properties of the cement with antibiotics are similar with those of the regular cement, when low doses of antibiotics are used and become more evident as the doses go up. In conclusion, the antibiotic bone cement is a trustworthy tool in the surgeon’s arsenal against infection, with minimal detriments from the mechanical view.

The influence of cell morphology on the compressive fatigue behavior of Ti-6Al-4V meshes fabricated by electron beam melting

Additive manufacturing technique is a promising approach for fabricating cellular bone substitutes such as trabecular and cortical bones because of the ability to adjust process parameters to fabricate different shapes and inner structures. Considering the long term safe application in human body, the metallic cellular implants are expected to exhibit superior fatigue property. The objective of the study was to study the influence of cell shape on the compressive fatigue behavior of Ti-6Al-4V mesh arrays fabricated by electron beam melting. The results indicated that the underlying fatigue mechanism for the three kinds of meshes (cubic, G7 and rhombic dodecahedron) is the interaction of cyclic ratcheting and fatigue crack growth on the struts, which is closely related to cumulative effect of buckling and bending deformation of the strut. By increasing the buckling deformation on the struts through cell shape design, the cyclic ratcheting rate of the meshes during cyclic deformation was decreased and accordingly, the compressive fatigue strength was increased. With increasing bending deformation of struts, fatigue crack growth in struts contributed more to the fatigue damage of meshes. Rough surface and pores contained in the struts significantly deteriorated the compressive fatigue strength of the struts. By optimizing the buckling and bending deformation through cell shape design, Ti-6Al-4V alloy cellular solids with high fatigue strength and low modulus can be fabricated by the EBM technique.

Effect of Solute Oxygen on Compressive Fatigue Strength of Spinal Fixation Rods Made of Ti–29Nb–13Ta–4.6Zr Alloys

In spinal fixation devices, the activity of the patient can cause fretting of the metal-to-metal contacts between the rod and plug, which may result in failures. In this study, compressive fatigue tests were conducted with rods made of Ti–29Nb–13Ta–4.6Zr alloy (TNTZ) with oxygen contents of 0.06 mass% (06O) and 0.89 mass% (89O) and Ti–6Al–4V extra low interstitial alloy (Ti64) as comparison in both air and saline solution. The fatigue strength increases in the order of 06O < 89O < Ti64 in both air and saline solution. These results indicate that solid-solution strengthening by oxygen improves the fretting fatigue resistance of the TNTZ rod.

Compressive fatigue behavior of low velocity impacted and quasi-static indented CFRP laminates

The compression fatigue behaviors of CFRP laminates with impacted or quasi-static indented damage for two material systems, CCF300/QY9511 and CCF300/5428, were compared in this paper. The same surface damages, characterized by dent depth, were induced by low velocity impact (LVI) or quasi-static indentation (QSI) tests for the CFRP laminates. Using visual observation, C-Scan and thermal de-ply experimental measure methods, the surface damage and internal delamination of the specimens are described in detail to provide more information to understand the mechanical behaviors of impacted or quasi-static indented CFRP laminates. Static tests and staircase fatigue tests were performed to obtain the static compressive strength and compressive fatigue strength. The experimental outcomes show that the compressive fatigue strength of the quasi-static indented specimens is obviously greater than that of impacted specimens, while the specimens with quasi-static indented damages have a similar static compressive strength as those with impacted damages, for both material systems. Using QSI-induced damage to replace LVI-induced damage provides a roughly equivalent strength evaluation in static compression tests but exaggerates fatigue strength estimation in compression fatigue tests.

VHCF Properties of A7075-T651 Al Alloy Depending on Shot Peening and Fatigue Testing Methods

Fatigue characteristics of A7075-T651 aluminum material were studied with surface treatment of shot peening. The fatigue life was characterized by two fatigue testing methods, ultrasonic fatigue test (UFT, 20 kHz) and the rotary-bending fatigue test (RFT, 53 Hz). The fatigue life improvement was confirmed by rotary bending fatigue tester. However, the surface modification effects were hardly observed by UFT method. The RFT results validate that the fatigue properties of RFT show a fine congruence regardless of the test machine types. The results of hardness, compressive residual stress, fatigue strength, and mechanical properties of specimen were improved by shot peening.

내부 원추형 연결형태 임플란트에서 지대주 나사머리의 좌면각도가 연결부 기계적 안정성에 미치는 영향

목적: 내부 원추형 연결형태 임플란트에서 지대주 나사의 좌면각도가 연결부의 기계적 안정성에 미치는 영향을 알아보기 위함이다. 연구 재료 및 방법: 원추형 연결구조 티타늄 임플란트와 시멘트 유지형 지대주, 텅스텐 카바이드 코팅된 티타늄 합금 지대주 나사를 사용하였다. 좌면각도가 <TEX>$45^{\circ}$</TEX>와 <TEX>$90^{\circ}$</TEX>를 갖는 지대주와 지대주 나사를 제작하여 30 Ncm 조임회전력으로 지대주를 체결한 후 하중을 가하고 체결 및 하중 부여에 따른 침하량을 측정하였다(n = 5). 유압식 피로시험기에 임플란트를 고정하고 스테인리스 스틸 금속관을 지대주에 합착하였다. 이 후 반복 하중을 가한 후 풀림토크 변화량을 측정하고, 압축굽힘강도와 피로강도를 측정하였다(n = 5). 결과: 지대주 침하량은 지대주나사 체결 시 가장 크게 나타났으며(P < 0.05), 나사체결과 하중부여에 따른 총 침하량은 <TEX>$45^{\circ}$</TEX>군보다 <TEX>$90^{\circ}$</TEX>군에서 더 크게 측정되었다(P < 0.05). 반복하중 부여 후 풀림 토크, 그리고 최대 압축굽힘강도와 피로강도는 통계적으로 유의한 차이를 보이지 않았다(P > 0.05). 결론: 본 실험조건하에서 지대주 나사머리의 원추형 설계가 지대주의 총 침하량을 약간 감소시키는 효과를 나타냈으나, 연결부의 전체적인 기계적 안정성에 미치는 영향은 크지 않을 것으로 판단된다. This study is to evaluate how different bearing surface angles of abutment screw affect the mechanical stability of the joint in the conical seal design implant system. Materials and Methods: Internal connection type regular implants, two-piece cemented type abutments and tungsten carbide/carbon-coated titanium alloy abutment screws were selected. Titanium alloy screws with conical (<TEX>$45^{\circ}$</TEX>) and flat (<TEX>$90^{\circ}$</TEX>) head designs which fit on to abutment were fabricated. The abutments were tightened to implants with 30 Ncm by digital torque gauge. The loading was applied once to the central axis of abutment. The mean axial displacement was measured using micrometer before and after the tightening and loading (n = 5). The abutment was tightened to implants with 30 Ncm and T-shape stainless steel crown was cemented. Then the change in the amount of reverse-torque was measured after the repeated loading to the central axis, and the place 5 mm away from the central axis. Compressive bending and fatigue strength were measured at the place 5 mm away from the central axis (n = 5). Results: Both groups showed the largest axial displacement when abutment screw tightening and total displacement was greater in the flat head group compared to conical head group (P < 0.05). However, there were no significant differences in reverse torque value, compressive bending and fatigue strength (P > 0.05). Conclusion: Within the limitations of this study, the abutment screw head design had no effect on two groups regarding the joint stability, however the conical head design affected the settlement of abutment resulting in the reduced total displacement.

Influence of Residual Stress on Fatigue Design of AISI 304 Stainless Steel

Austenitic stainless steel cannot be hardened by any form of heat treatment, in fact, quenching from 10000C merely softens them. They are usually cold worked to increase the hardness. Shot peening is a cold working process that changes micro-structure as well as residual stress in the surface layer. In the present work, the compressive residual stress and fatigue strength of AISI 304 austenitic stainless steel have been evaluated at various shot peening conditions. The improvement in various mechanical properties such as hardness, damping factors and fatigue strength was noticed. Compressive residual stress induced by shot peening varies with cyclic loading due to relaxation of compressive residual stress field. The consideration of relaxed compressive residual stress field instead of original compressive residual stress field provides reliable fatigue design of components. In this paper, the exact reductions in weight and control of mechanical properties due to shot peening process are discussed.

Mechanical and Biomechanical Characterization of a Polyurethane Nucleus Replacement Device Injected and Cured In Situ Within a Balloon

Background The DASCOR device has recently been introduced as an innovative nucleus replacement alternative for the treatment of low-back pain caused by degenerative intervertebral disc disease. The purpose of this study was to characterize, through a series of preclinical mechanical bench and biomechanical tests, the effectiveness of this device. Methods A number of samples were created using similar preparation methods in order to characterize the nucleus replacement device in multiple mechanical bench tests, using ASTM-guided protocols, where appropriate. Mechanical bench testing included static testing to characterize the device's compressive, shear properties, and fatigue testing to determine the device's compressive fatigue strength, wear, and durability. Biomechanical testing, using human cadaveric lumbar spines, was also conducted to determine the ability of the device to restore multidirectional segmental flexibility and to determine its resulting endplate contact stress. Results The static compressive and shear moduli of the nucleus replacement device were determined to be between 4.2–5.6 MPa and 1.4–1.9 MPa, respectively. Similarly, the ultimate compressive and shear strength were 12,400 N and 6,993 N, respectively. The maximum axial compressive fatigue strength of the tested device that was able to withstand a runout without failure was determined to be approximately 3 MPa. The wear assessment determined that the device is durable and yielded minimal wear rates of 0.29mg/Mc. Finally, the biomechanical testing demonstrated that the device can restore the multidirectional segmental flexibility to a level seen in the intact condition while concurrently producing a uniform endplate contact stress. Conclusions The results of the present study provided a mechanical justification supporting the clinical use of the nucleus replacement device and also help explain and support the positive clinical results obtained from two European studies and one US pilot study. Clinical Relevance Nucleus replacement devices are rapidly emerging to address specific conditions of degenerative disc disease. Preclinical testing of such devices is paramount in order to potentially ensure successful clinical outcomes post implantation

Mechanical and biomechanical characterization of a polyurethane nucleus replacement device injected and cured in situ within a balloon.

BackgroundThe DASCOR device has recently been introduced as an innovative nucleus replacement alternative for the treatment of low-back pain caused by degenerative intervertebral disc disease. The purpose of this study was to characterize, through a series of preclinical mechanical bench and biomechanical tests, the effectiveness of this device.MethodsA number of samples were created using similar preparation methods in order to characterize the nucleus replacement device in multiple mechanical bench tests, using ASTM-guided protocols, where appropriate. Mechanical bench testing included static testing to characterize the device's compressive, shear properties, and fatigue testing to determine the device's compressive fatigue strength, wear, and durability. Biomechanical testing, using human cadaveric lumbar spines, was also conducted to determine the ability of the device to restore multidirectional segmental flexibility and to determine its resulting endplate contact stress.ResultsThe static compressive and shear moduli of the nucleus replacement device were determined to be between 4.2–5.6 MPa and 1.4–1.9 MPa, respectively. Similarly, the ultimate compressive and shear strength were 12,400 N and 6,993 N, respectively. The maximum axial compressive fatigue strength of the tested device that was able to withstand a runout without failure was determined to be approximately 3 MPa. The wear assessment determined that the device is durable and yielded minimal wear rates of 0.29mg/Mc. Finally, the biomechanical testing demonstrated that the device can restore the multidirectional segmental flexibility to a level seen in the intact condition while concurrently producing a uniform endplate contact stress.ConclusionsThe results of the present study provided a mechanical justification supporting the clinical use of the nucleus replacement device and also help explain and support the positive clinical results obtained from two European studies and one US pilot study.Clinical RelevanceNucleus replacement devices are rapidly emerging to address specific conditions of degenerative disc disease. Preclinical testing of such devices is paramount in order to potentially ensure successful clinical outcomes post implantation

Damage tolerance and durability of selectively stitched stiffened composite structures

Through-the-thickness stitching is one of the promising approaches to improve the impact damage tolerance of stiffened composite structures. In this research, the effect of selective stitching on impact damage tolerance and fatigue durability of stiffened composite panels was extensively investigated and compared with unstitched stiffened composite panels. Two-blade stiffened composite panels were fabricated by resin film infiltration technique. Impact damage was inflicted on the stiffened panels using a drop-weight with the impact energy of 30 J from the skin-side over the stiffener and the flange. The experimental results indicate that selective stitching is an effective way to improve the compressive failure strength and fatigue strength of stiffened panels with both clearly visible flange damage (CVFD) and clearly visible stiffener damage (CVSD). The bulking and post-buckling finite element analyses were performed to predict the static compressive strength of the selectively stitched stiffened panels. A good agreement was obtained between analytical and experimental results. The failure behaviors of the undamaged, CVFD and CVSD panels were also investigated.

Compressive Fatigue Strength and Fracture Mechanism of Giant Magnetostrictive Materials Fabricated by Powder Metallurgy

This paper deals with the compressive strength of Terfenol-D type giant magnetostrictive materials fabricated with the powder metallurgy. Static and fatigue compressive tests for the specimens with different porosity were performed. Static compressive tests indicated that the compressive strength of this material can be estimated with the porosity and strength of dense material with same components. Compressive fatigue tests with the same specimens showed that the compressive fatigue strength of this material is 90% to the static compressive strength. Observations of cracks in the specimens were carried out before and after compressive loading. The effects of the compressive stress to the numbers and length of the cracks were examined. Observations showed significant increase of the number of the cracks with length of 5 to 20μm after static and fatigue compressive loading. Fracture processes for static and cyclic loading were proposed.